I. Technical Field
The present invention relates to a disc cartridge and a photon mode optical information recording/reproducing apparatus used for recording/reproducing photon mode optical information.
II. Description of the Related Art
A common disc-shaped recording medium (hereinafter, referred to as a medium) represented by magnetooptical recording or phase change recording is rotatably contained in a disc case. The disc case includes an opening section through which the outer surface of the medium is exposed and a slidable shutter for opening and closing the opening section.
Since an optical disc information recording/reproducing apparatus records and reproduces information by substantially focusing a laser light to a diffraction limit, information recording/reproducing characteristics are degraded upon an occurrence of dust adherence or accumulation to or on the outer surface of the medium. Particularly, since the medium features in being portable and providing compatibility among information recording/reproducing apparatuses, it has been a big problem to prevent the intrusion of dust into the case or the adherence of dust to the outer surface of the medium outside the information recording/reproducing apparatuses. Accordingly, a great number of proposals have been made such as those to improve dust resistance and those concerning the construction of disc cases and disc cartridges to prevent damage on recording surfaces of media, for example, as disclosed in Japanese Unexamined Patent Publication No. 2000-40331 and Japanese Unexamined Patent Publication No. 2004-14115.
On the other hand, a photon mode optical information recording/reproducing apparatus has been proposed as a candidate for a next-generation large-capacity storage device. The photon mode optical information recording/reproducing apparatus adopts recording and reproducing methods different from the conventional optical disc devices, and a hologram memory device, for example, as disclosed in Japanese Unexamined Patent Publication No. 2004-139711 can be cited as a typical example. In a hologram memory optical information recording system such as a hologram memory optical system adopting a shift multiplexing recording method proposed by Psaltis et al., a beam from a laser light source has its diameter expanded by a beam expander and, then, this beam is split by a half mirror. One of the split beams passes a spatial light modulator and is focused on a hologram medium by a Fourier transform lens to become a signal light. The other beam is irradiated to the same position as the signal light on the hologram medium to become a reference light. The hologram medium is constructed such that a holographic medium such as photopolymer is sealed between two glass substrates, and interference fringes of the signal light and reference light are recorded.
In the spatial light modulator, a two-dimensionally arranged optical switch array is provided, and the respective optical switches are independently turned on and off in accordance with an input signal to be recorded. For example, in the case of using a spatial light modulator of 1024 cells×1024 cells, information of 1 M bits can be simultaneously displayed. The information of 1 M bits displayed on the spatial light modulator when a signal light passes the spatial light modulator is converted into a two-dimensional light beam array. This light beam array is recorded as interference fringes on the hologram medium. In order to reproduce the recorded signal, only the reference light is irradiated to the hologram medium and a diffracted light from a hologram is received by a CCD element.
The aforementioned hologram memory optical information recording system is characterized in that angle multiplexing recording is possible to realize a large-capacity optical recording system since the holographic medium is as thick as about 1 mm and the interference fringes are recorded as a thick grating, i.e. a so-called Bragg grating. Instead of changing an incident angle of the reference light, it is also possible to realize angle multiplexing recording by shifting the irradiation position of the reference light in the form of a spherical wave. Specifically, there are utilized slight changes in the incident angle of the reference light sensed by the respective parts of the medium upon shifting the recording position by slightly rotating the disc-shaped medium. When the thickness of the holographic medium is 1 mm, wavelength selectivity specified by the intensity of the reproduced signal is 0.014 degrees at full width at half maximum. When the reference light NA is 0.5 and the hologram size is 2 mmφ, recording density realized at this time is 600 G bits/inch2 if a hologram is recorded in a multiplexing manner at intervals of about 20 microns. This is equivalent to 730 GB in a 12 cm disc capacity.
Japanese Unexamined Patent Publication No. 2004-362743 shows a holographic disc cartridge. A Japanese Unexamined Patent Publication No. 2004-362743 discloses a locking mechanism for preventing an inadvertent opening of a slide shutter.
A medium used in the optical information recording/reproducing apparatus with an optical photon mode is made of a so-called photosensitive material in the nature of the recording method. Thus, this medium has sensitivity to lights having wavelengths below a visible light region such as ultraviolet rays and green lights. If a non-recorded area of the medium is photosensitized before recording, this has presented a problem of fatally degrading the characteristics such as a reduction of a recordable capacity. Although the disc cartridges for optical discs (magnetooptical discs, CDs, DVDs, etc.) disclosed in Japanese Unexamined Patent Publication No. 2000-40331 and Japanese Unexamined Patent Publication No. 2004-14115 have effective constructions in terms of dust resistance, it is substantially impossible to optically completely shield the media since there is no concept of complete shielding. Thus, if an attempt is made to apply the disc cartridge construction for optical discs to those used in photon mode optical information recording/reproducing apparatuses, there has been a problem of causing the above characteristic degradation, for example, by a stray light entering through a clearance between the slide shutter and the cartridge case. Although it is disclosed that the slide shutter slides relative to a cartridge shell in the disc cartridge of Japanese Unexamined Patent Publication No. 2004-362743, there is a possibility of creating a clearance between the cartridge shell and slide shutter due to the vibration of the slide shutter or the like since the slide shutter is merely placed on the cartridge shell. Accordingly, complete light shielding is difficult in this disc cartridge.